The character is rather a bit introverted, so realistically it should probably be the left one. However I was thinking whether the left one is sexy enough? Or is that something you not really care about for the playable character (and more/only for the romance-able chars)?

I can't judge on the sexiness, but sometimes sexy comes off better when they aren't purposefully trying? If he's introverted the first image is probably better, the second image doesn't look introverted at all, but more like a really confident guy.

Well, I know a lot of people doesn't look like how they act, myself included, I looked introverted in the past but people said that I was extraverted, another time in my life it was the contrary , and other time my look match what people think of me.

and personnaly I care about the look of the PC , what is better than a sexy romance option, two...euh a sexy romance option with a sexy PC... .

seriously...if you ask which protagonist I want in a VN I will choose the one I like the most so in general the least "ukish".